Live vector vaccines can serve as a practical and effective component in the defense strategy against agents of biological attack. In this U19 Cooperative Agreement, we will develop several live attenuated vaccines which can serve as prophylactic agents unto themselves, but will also comprise highly effective priming agents to increase the efficacy of parenteral subunit vaccines. In this project, we will specifically assess the ability of mucosal Salmonella and V. cholerae live vector strains expressing protective antigens from B. anthracis, Y. pestis, and C. botulinum to prime immune responses that can be rapidly boosted by parenterally delivered subunit vaccines. Based on available data, a single dose of an appropriate mucosally delivered live vector vaccine is expected to prime systemic and mucosal immune responses that will be further enhanced and broadened by a subsequent dose of parenterally delivered purified antigen. Priming with bacteria-expressed antigens will likely augment Th-1-biased responses, whereas a parenteral boost with purified antigen and adjuvant will increase primarily Th-2 reponses. Thus, the primary goal of this component is to evaluate the immune responses induced by mucosally delivered Salmonella and V. cholerae expressing protective antigens from B. anthracis, Y. pestis, and C. botulinum when used in combination with parenteral subunit vaccines in a prime -boost approach. These studies will be critical to understand the potential of the products developed under this U19, and to determine the most effective way to employ them. Thus, this project will can be considered "value added" for the other four projects.